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Zagros Mountains

The Zagros Mountains (Persian: کوه‌های زاگرس‬‎; Kurdish: چیاکانی زاگرۆس‬‎) form the largest mountain range in Iran, Iraq and southeastern Turkey. This mountain range has a total length of 1,500 km (930 mi). The Zagros mountain range begins in northwestern Iran and roughly corresponds to Iran's western border. It spans the whole length of the western and southwestern Iranian plateau, ending at the Strait of Hormuz. The highest point is Mount Dena.

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The Zagros fold and thrust belt was formed by the collision of two tectonic plates, the Eurasian Plate and the Arabian Plate.[3] This collision primarily happened during the Miocene and folded the entire rocks that had been deposited from the Carboniferous to the Miocene in the geosyncline in front of the Iranian Plate. The process of collision continues to the present and as the Arabian Plate is being pushed against the Eurasian Plate, the Zagros Mountains and the Iranian Plateau are getting higher and higher. Recent GPS measurements in Iran[4] have shown that this collision is still active and the resulting deformation is distributed non-uniformly in the country, mainly taken up in the major mountain belts like Alborz and Zagros. A relatively dense GPS network which covered the Iranian Zagros[5] also proves a high rate of deformation within the Zagros. The GPS results show that the current rate of shortening in the southeast Zagros is ~10 mm/a (0.39 in/year), dropping to ~5 mm/a (0.20 in/year) in the northwest Zagros. The north-south Kazerunstrike-slip fault divides the Zagros into two distinct zones of deformation. The GPS results also show different shortening directions along the belt, normal shortening in the southeast and oblique shortening in the northwest Zagros. The Zagros mountains were created around the time of the second ice age, which was the reason for the crashing of the tectonic plates, leading to it's uniqueness.

The sedimentary cover in the SE Zagros is deforming above a layer of rock salt (acting as a ductiledecollement with a low basal friction) whereas in the NW Zagros the salt layer is missing or is very thin. This different basal friction is partly responsible for the different topographies on either side of the Kazerun fault. Higher topography and narrower zone of deformation in the NW Zagros is observed whereas in the SE, deformation was spread more and a wider zone of deformation with lower topography was formed.[6] Stresses induced in the Earth's crust by the collision caused extensive folding of the preexisting layered sedimentary rocks. Subsequent erosion removed softer rocks, such as mudstone (rock formed by consolidated mud) and siltstone (a slightly coarser-grained mudstone) while leaving harder rocks, such as limestone (calcium-rich rock consisting of the remains of marine organisms) and dolomite (rocks similar to limestone containing calcium and magnesium). This differential erosion formed the linear ridges of the Zagros Mountains. The depositional environment and tectonic history of the rocks were conducive to the formation and trapping of petroleum, and the Zagros region is an important area for oil production. Salt domes and salt glaciers are a common feature of the Zagros Mountains. Salt domes are an important target for petroleum exploration, as the impermeable salt frequently traps petroleum beneath other rock layers.

The mountains have a totally sedimentary origin and are made primarily of limestone. In the Elevated Zagros or the Higher Zagros, the Paleozoic rocks could be found mainly in the upper and higher sections of the peaks of the Zagros Mountains along the Zagros main fault. On both sides of this fault, there are Mesozoic rocks, a combination of Triassic and Jurassic rocks that are surrounded by Cretaceous rocks on both sides. The Folded Zagros (the mountains south of the Elevated Zagros and almost parallel to the main Zagros fault) is formed mainly of Tertiary rocks, with the Paleogene rocks south of the Cretaceous rocks and then the Neogene rocks south of the Paleogene rocks. The mountains are divided into many parallel sub-ranges (up to 10 or 250 km (6.2 or 155.3 mi) wide), and orogenically have the same age as the Alps. Iran's main oilfields lie in the western central foothills of the Zagros mountain range. The southern ranges of the Fars Province have somewhat lower summits, reaching 4,000 metres (2.5 miles). They contain some limestone rocks showing abundant marine fossils.[citation needed]

The mountains of the East-Zagros, the Kuh-i-Jupar (4,135 m (13,566 ft)), Kuh-i-Lalezar (4,374 m (14,350 ft)) and Kuh-i-Hezar (4,469 m (14,662 ft)) do not currently have glaciers. Only at Zard Kuh and Dena some glaciers still survive. However, before the Last Glacial Period they had been glaciated to a depth in excess of 1,900 metres (1.2 miles), and during the Last Glacial Period to a depth in excess of 2,160 metres (7,090 feet). Evidence exists of a 20 km (12 mi) wide glacier fed along a 17 km (11 mi) long valley dropping approximately 1,500 m (4,900 ft) along its length on the north side of Kuh-i-Jupar with a thickness of 350–550 m (1,150–1,800 ft). Under precipitation conditions comparable to the current conditions, this size of glacier could be expected to form where the annual average temperature was between 10.5 and 11.2 °C (50.9 and 52.2 °F), but since conditions are expected to have been dryer during the period in which this glacier was formed, the temperature must have been lower.[7][8][9][10]

The mountains contain several ecosystems. Prominent among them are the forest and forest steppe areas with a semi-arid climate. As defined by the World Wildlife Fund and used in their Wildfinder, the particular terrestrial ecoregion of the mid to high mountain area is Zagros Mountains forest steppe (PA0446). The annual precipitation ranges from 400–800 mm (16–31 in) and falls mostly in winter and spring. Winters are severe, with low temperatures often below −25 °C (−13 °F). The region exemplifies the continental variation of the Mediterranean climate pattern, with a snowy winter and mild, rainy spring, followed by a dry summer and autumn.[11]

Although currently degraded through overgrazing and deforestation, the Zagros region is home to a rich and complex flora. Remnants of the originally widespread oak-dominated woodland can still be found, as can the park-like pistachio/almond steppelands. The ancestors of many familiar foods, including wheat, barley, lentil, almond, walnut, pistachio, apricot, plum, pomegranate and grape can be found growing wild throughout the mountains.[14]Persian oak (Quercus brantii) (covering more than 50% of the Zagros forest area) is the most important tree species of the Zagros in Iran.[15]

Signs of early agriculture date back as far as 9000 BC to the foothills of the mountains,[19] in cities later named Anshan and Susa. Jarmo is one archaeological site in this area. Shanidar, where the ancient skeletal remains of Neanderthals have been found, is another. Some of the earliest evidence of wine production has been discovered in the mountains; both the settlements of Hajji Firuz Tepe and Godin Tepe have given evidence of wine storage dating between 3500 and 5400 BC.[20]